Establishment and verification of time-temperature integrators for Chinese cuisine

Abstract: Chinese cuisine is regarded as a kind of traditional artistry that has multiple genres, various cooking methods and complicated cooking skills. Stir-frying, a typical operation in Chinese cuisine, normally has the characteristics of short time and drastic stirring. Due to the drastic stirring, food particles rapidly move, so common research methods cannot be used to investigate the internal temperature-time relationship of particles in liquid-particle heat transfer process by this operation, such as the thermocouple method and the numerical simulation method, both of which are limited to determine heat transfer coefficient. In order to realize the standardization and automation of Chinese cuisine, it is necessary to master the changing rules of heat transfer and quality during cooking process, and therefore, time-temperature integrators (TTIs) and the corresponding heat transfer - kinetics mathematical model are crucial or even indispensable methods for the researches on quality changes of cooking. The time-temperature integrator, a small equipment composed of an indicator and a carrier, was used to simulate the changes of target quality parameters, time and temperature history as well as food analogues. Therefore, the indicator must have key quality factors that are similar to kinetic parameters in real food materials, and the shape of food analogues must have similar thermal physical properties to real food system. Protein denaturation is widely used to represent quality changes in cooking process. Surprisingly, a kind of thermostable α amylase with the similar z value (7.36 ℃) to protein denaturation (5-10 ℃) was discovered and successfully applied as an indicator in our experiment. Specifically, the indicator was encapsulated in a capillary tube and then embedded in a carrier with particular shape for establishing TTIs. The carrier was made of konjac glucomannan gel (g-KGM) which has superior heat resisting property. Subsequently, to simulate cooking process of liquid-particle food under the specific heat transfer condition, the changes of enzyme activity were determined by TTIs, and the theoretical temperature-time relationship was calculated with the unsteady heat transfer mathematical model and then compared with practical experimental results. The temperature curve with the minimal gap of theoretical and actual value was obtained on the basis of the least. Summation of the squared temperature difference for overall target (LSTD). Finally, the residual activity of α amylase was obtained based on kinetics methods. And the difference with the measured enzyme activity was not more than 2.24%, indicating the TTIs mathematical model was accurate and reliable. Furthermore, the TTIs mathematical model was used to determine the heat transfer coefficient during stir-frying process of Chinese cuisine. The results showed that the TTIs combined with numerical simulation was appropriate for analyzing and measuring heat transfer process, even for the situations conventional heat transfer experiment method was powerless or some other stormy cooking process with liquid-particle. In addition, armed with quality change kinetics, the heat transfer could be analyzed especially for heated treatment of liquid-particle. That is to say, this method may provide key technology for procedure analysis and process optimization of Chinese cuisine. Moreover, it can also be applied to those studies on actual heat transfer process of moving particles in other field.